This invention relates to an improved radially expansible tire assembly drum (10) and a method for forming tires (2) from an assemblage of tire components utilizing the assembly drum (10).
Historically, the pneumatic tire has been fabricated as laminated structure of generally toroidal shape having beads, a tread, a belt reinforcement and carcass. The tire is made of rubber, fabric, and steel. The manufacturing technologies employed for the most part involve assembling the many tire components from flat strips or sheets of material. Each component is placed on a building drum and cut to length such that the ends of a component meet, or overlap, creating a splice.
In the first stage of assembly, the carcass would include one or more plies, and a pair of sidewalls, a pair of apexes, an inner liner (for a tubeless tire), a pair of chafers and perhaps a pair of gum shoulder strips. Annular bead cores can be added during the first stage of tire building, and the ply or plies can be turned around the bead cores to form the xe2x80x9cply turnups.xe2x80x9d
Typically, the carcass components (excluding the bead cores) would be either xe2x80x9cbutt splicedxe2x80x9d or xe2x80x9clap spliced.xe2x80x9d A butt splice has the component ends joined, but not overlapped. A lap splice has overlapping ends.
This intermediate article of manufacture can be cylindrically formed at this point in the first stage of assembly. The cylindrical carcass is expanded into a toroidal shape after completion of the first-stage of tire building. Reinforcing belts and the tread are added to the intermediate article during a second stage of tire manufacture, which can occur using the same building drum or work station or at a separate shaping station.
During the expansion of the carcass, tensile stresses are imposed on the spliced and uncured components of the tire carcass.
In the case of automobile or light truck tires, lap splices were preferred because the splice remained intact, whereas butt splices would tend to open or fail. Even with the good adhesion of the lap splice, the cords adjacent the splice tended to be stretched compensating for the overlapped two layers of cords at the splice. This localized stretching creates a non-uniformity that is readily visible under x-ray, ultrasonic display or by physically cutting the tire and visually inspecting it.
The tire designer, in order to prevent the creation of tire uniformity problems, has historically insured that the splices of various layers of components were not circumferentially aligned. This non-alignment of splice joints was believed to improve the carcass overall durability and uniformity, as measured by the amount of force variation and the balance of the tire. Tire engineers also have believed that tire uniformity could be improved if these discontinuities were deliberately circumferentially spaced around the carcass. This meant that each component had to be applied to the ply at the tire building station where each component was cut and spliced in a spaced order.
When the cord reinforced plies are placed on the building drum, it is very important that the geometric spacing of the beads and the ply turnups are controlled a uniformly. Variations in the overall tire building process can result in variations in cord tension. These non-uniformities can affect the ride and handling characteristics of the tire.
In U.S. Pat. No. 6,250,356 to Michelin, a tire assembly drum is disclosed wherein the beads are two distinct sizes. Conventionally, tires are symmetrical having equal bead diameters. The two distinct diameters on a tire exacerbate the problems of tire building and the disclosed assembly drum provides a method and apparatus to permit the tire to be built in a more uniform and faster way. This building drum was designed to build tires having a given set of two different diameters at the first stage of assembly. A separate tire-shaping drum was used to toroidally shape the tire carcass to assemble the tread and belt reinforcements and that drum is disclosed in U.S. Pat. No. 6,234,227.
The present invention has the objective of providing a building drum that is radially expansible and capable of building tires of equal bead diameters or of different bead diameters over a range of diameter sizes. In one embodiment, the building drum further has the objective of having axially movable ends, which can be air tightly sealed to permit the assembled carcass to be inflated and shaped toroidally, avoiding removal from the assembly drum for a second stage of tire building.
An improved radially expansible assembly drum for the manufacture of tires is disclosed. The assembly drum has a body mounted on a drum core assembly and presenting a receiving surface for tire components to be assembled. The ends and the receiving surface have the same or different diameters. A means for covering the ends of the receiving surface and a means for radially expanding the drum are also provided. The means for radially expanding the drum includes the ability to radially expand the receiving surface at the center and the ends of the assembly drum.
The radially expansible assembly drum has the means for radially expanding the assembly drum, including a cam disk having an increasing spiral cam follower groove. The cam follower groove provides a continuous range of selectable diameters and stable expansion of the drum diameters as a function of cam disk rotation. The spiral cam follower groove radially increases or decreases, dependent on the direction of rotation, causing an increase or a decrease in diametrical expansion or contraction at a rate of 40 mm per 360xc2x0 of rotation of the assembly drum. The continuous range of selectable diameters increases from a diameter of di to a fully expanded diameter de, de being equal to or greater than di+55 mm.
In one embodiment of the invention, the radially expandable assembly drum has a means for axially moving the ends of the assembly drum, the ends being simultaneously movable from an axially widely spaced location to an axially inner location closer to a centerline of the assembly drum. This movement of the two ends is preferably equal in axial displacement. This reduction in axial space between the two ends permits the cords of the ply to be radially expanded and the assembled tire carcass to be toroidally shaped to permit the tread and reinforcing belt structure to be assembled while the assembled tire is held on the radially expansible assembly drum.
The multi-movement capability of the assembly drum is achieved by this unique drum core assembly. The drum core assembly includes a spindle for rotating the assembly drum, a driving shaft which passes through the center of the spindle, and a first external shaft connected to the means for radially expanding the assembly drum. The first external shaft is parallel and eccentrically located relative to the centerline of the spindle. The driving shaft provides rotary motion to the first external shaft, via a first external clutch mechanism. The engagement of the first clutch mechanism rotates the first external shaft to initiate radial expansion or contraction of the drum assembly.
The drum core assembly further includes a second external shaft connected to the means for axially moving the ends of the assembly drum. The second external shaft is parallel to and eccentrically located relative to the centerline of the spindle. The second external shaft is connected to a second clutch mechanism. The engagement of the second clutch mechanism (to the driving shaft) rotates the second external shaft to initiate axial movement of the ends of the assembly drum.
The second external shaft has oppositely directed threads, one set of threads being connected to one end of the assembly drum, the oppositely directed threads being connected to the opposite end of the assembly drum. Rotation of the second external shaft in one rotating direction moves the ends of the assembly drum closer while an opposite rotation of the second external shaft moves the ends further apart.
Due to the fact the entire drum can be rotated by the spindle independent of the action of the first or second external shafts, means that the exact location of the drum assembly in terms of axial width, radial expansion, and angular rotation is not fixed absent a means for establishing these locations. The radially expansible assembly drum provides a three-way encoder means to provide exact locations of each position of assembly drum.
The encoder means includes three sensors for indicating the angular rotation of the drum core assembly. The three sensors indicate the angular rotation of the spindle, the first external shaft and the second external shaft, respectively. Each encoder has a sensor that is located in proximity to an annular disk, which is fixed to one of the shafts. The annular disk has a readable surface, which enables the sensor to detect the exact location of the respective shaft. The rotation of the shafts are sensed and fed back to a means for computing the angular position of each of the shafts relative to a pre-selected building sequence to initiate the movements of the drum assembly.
The preferred embodiment of the invention includes a means for inflating the assembled tire carcass while on the assembly drum for a second stage assembly of a tread and a belt reinforcing structure. In one embodiment, there is a means for moving one or both ends of the assembly drum relative to the other end. Additionally, the means for covering the ends of the receiving surface is preferably a flexible elastomeric membrane. The means for covering, the ends of the receiving surfaces form an airtight seal on each end of the assembly drum. This feature facilitates the inflating of the assembled tire component by creating airtight seals around the ends of the assembly drum Furthermore, the beads of the tire, by compressing the elastomeric means for covering the ends into depressions in the ends, insures the seals are maintained between the internal surfaces of the tire and the assembly drum.
Definitions
xe2x80x9cApexxe2x80x9d means an elastomeric filler located radially above the bead and interposed between the plies and the ply turn-up.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim.
xe2x80x9cBelt Structurexe2x80x9d or xe2x80x9cReinforcing Beltsxe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17xc2x0 to 27xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cCarcassxe2x80x9d means an unvulcanized laminate of tire ply material and other tire components cut to length suitable for splicing, or already spliced, into a cylindrical or toroidal shape. Additional components may be added to the carcass prior to its being vulcanized to create the molded tire.
xe2x80x9cCasingxe2x80x9d means the tire carcass and associated tire components excluding the tread.
xe2x80x9cChafersxe2x80x9d refers to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim, and to seal the tire.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands of which the plies in the tire are comprised.
xe2x80x9cEquatorial Plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cInnerlinerxe2x80x9d means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.
xe2x80x9cInsertxe2x80x9d means an elastomeric member used as a stiffening member usually located in the sidewall region of the tire.
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial Ply Tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cShoulderxe2x80x9d means the upper portion of sidewall just below the tread edge.
xe2x80x9cSidewallxe2x80x9d means that portion of a tire between the tread and the bead.
xe2x80x9cSubassemblyxe2x80x9d means an unvulcanized assembly of laminated tire components to which a cord reinforced ply or plies and other components can be added to form a tire carcass.
xe2x80x9cTreadxe2x80x9d means a rubber component which, when bonded to a tire carcass, includes that portion of the tire that come into contact with the road when the tire is normally inflated and under normal load.
xe2x80x9cTread Widthxe2x80x9d means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.